Hybrid serial counterflow dual refrigerant circuit chiller

ABSTRACT

A dual refrigerant circuit chiller ( 10 ) has a first refrigerant circuit ( 100 ) including a first condenser ( 130 ) and a first evaporator ( 140 ), a second refrigerant circuit ( 200 ) including a second condenser ( 230 ) and a second evaporator ( 240 ), a condenser assembly ( 30 ) including the first condenser ( 130 ) and the second condenser ( 230 ) interconnected in a series cooling fluid circuit, and an evaporator assembly ( 40 ) including the first evaporator ( 140 ) and the second evaporator ( 240 ) interconnected in a series fluid circuit with a waterbox ( 50 ) disposed intermediate the first evaporator ( 140 ) and the second evaporator ( 240 ). The evaporator assembly ( 40 ) has a chilled fluid inlet ( 45 ) and a chilled fluid outlet ( 43 ) that are disposed at opposite longitudinal ends of the evaporator assembly ( 40 ). Each of the first and second evaporators ( 140, 240 ) embodies a multiple pass circuit fluid-to-refrigerant heat exchanger.

FIELD OF THE INVENTION

This invention relates generally to dual circuit chillers and, moreparticularly, to the improvement in the waterside performance of a dualrefrigerant circuit chiller.

BACKGROUND OF THE INVENTION

Chillers are well known for use in providing chilled fluid, commonlywater or brine, for use in air conditioning systems for buildings,especially large commercial buildings. A common type of chiller includesa tube-in-shell heat exchanger that functions as a refrigerant vaporcondenser, a tube-in-shell heat exchanger that functions as arefrigerant liquid evaporator, and a centrifugal compressor that has aninlet in refrigerant flow communication with the evaporator and anoutlet in refrigerant flow communication with the condenser. In thecondenser, cooling fluid, most commonly, water is passed through theheat exchange tubes in heat exchange relationship with hot refrigerantvapor discharged from the compressor into the shell of the condenser andflowing over the heat exchange tubes. In doing so, the refrigerant vaporis condensed and the water flowing through the heat exchange tubes isheated. The condensed liquid refrigerant is passed through an expansiondevice and thereby expanded to form a lower pressure, lower temperaturerefrigerant liquid/vapor mixture. The refrigerant liquid/vapor mixtureis delivered into the shell of the evaporator and dispersed to flow overthe heat exchange tubes therein. In the evaporator, water passingthrough the heat exchange tubes is cooled and the refrigerantliquid/vapor mixture is heated and the liquid refrigerant evaporated.The refrigerant vapor exits the shell of the evaporator and passes backthe inlet of the compressor, thereby completing the refrigerant flowcircuit. The chilled water having traversed the evaporator heat exchangetubes is delivered to the building air conditioning system for coolingair to be supplied to a climate-controlled space or spaces within thebuilding.

In one-type of chiller, commonly termed a single pass, single circuitchiller, a single water-cooled condenser, a single centrifugalcompressor and single water-chilling evaporator are connected in asingle refrigerant circuit as described above. In the condenser, aplurality of parallel water-conveying tubes extends longitudinally inparallel to the axis of the condenser shell in a single-passarrangement. Similarly, in the evaporator, a plurality of parallelwater-conveying tubes extends longitudinally in parallel to the axis ofthe condenser shell in a single-pass arrangement. Typically, the waterto chilled passing through the single-pass tubes of the evaporatorpasses in counterflow relationship to the cooling water passing throughthe single-pass tubes of the condenser. However, the water-chillingcapability that can be obtained with a single-pass, single-circuitchiller is limited.

One approach to increasing water-chilling capacity is to provide a dualcircuit chiller consisting of two single pass, single circuit chillersarranged with their respective refrigerant circuits in parallelarrangement and the water passes of the respective condensers and of therespective evaporators connected in series relationship. Again the waterto be chilled passing through the single pass tubes of the evaporatorspasses in counterflow relationship to the cooling water passing throughthe single-pass tubes of the condensers. Thus, the water to be chilledpasses first through the condenser associated with the first refrigerantcircuit and thence through the condenser associated with the secondrefrigerant circuit, but the cooling water passes first through theevaporator associated with the second refrigerant circuit and thencethrough the evaporator associated with the first refrigerant circuit.

SUMMARY OF THE INVENTION

In an aspect of the invention, a dual refrigerant circuit chiller isprovided having a first refrigerant circuit including a first condenserand a first evaporator; a second refrigerant circuit including a secondcondenser and a second evaporator, a condenser assembly including thefirst condenser and the second condenser interconnected in a seriescooling fluid circuit, and an evaporator assembly including the firstevaporator and the second evaporator interconnected in a series fluidcircuit and a waterbox disposed intermediate the first evaporator andthe second evaporator. The condenser assembly has a cooling fluid inletin fluid communication with the second condenser and a cooling fluidoutlet in fluid communication with the first condenser. The evaporatorassembly has a circuit fluid inlet in fluid communication with the firstevaporator and a circuit fluid outlet in fluid communication with thesecond evaporator. The circuit fluid inlet and the circuit fluid outletare disposed at opposite longitudinal ends of the evaporator assembly.In an embodiment the first evaporator has a multiple pass circuitfluid-to-refrigerant heat exchanger having an outlet in fluidcommunication with the waterbox and an inlet in fluid communication withthe circuit fluid inlet of the evaporator assembly, and the secondevaporator has a multiple pass circuit fluid-to-refrigerant heatexchanger having an inlet in fluid communication with the waterbox andan outlet in fluid communication with the circuit fluid outlet of theevaporator assembly. In an embodiment, the circuit fluid-to-refrigerantheat exchanger of the first evaporator and the circuitfluid-to-refrigerant heat exchanger of the second evaporator eachcomprise a three pass tube bundle heat exchanger.

In an aspect of the invention, a dual circuit chiller is provided havinga first refrigerant circuit including a first condenser and a firstevaporator; a second refrigerant circuit including a second condenserand a second evaporator, a condenser assembly including the firstcondenser and the second condenser interconnected in a series coolingfluid circuit with a cooling fluid inlet in fluid communication with thesecond condenser and a cooling fluid outlet in fluid communication withthe first condenser; and an evaporator assembly including the firstevaporator and the second evaporator interconnected in a series fluidcircuit and a waterbox disposed intermediate the first evaporator andthe second evaporator, the waterbox having a first chamber, a secondchamber and a third chamber. The evaporator assembly has a circuit fluidinlet and the circuit fluid outlet disposed at opposite longitudinalends of the evaporator assembly, a first bypass conduit having an inletin fluid communication with the circuit fluid inlet of the evaporatorassembly and an outlet in fluid communication with the first chamber ofthe waterbox; a first multiple pass circuit fluid-to-refrigerant heatexchanger disposed in the first evaporator having an inlet in fluidcommunication with the first chamber of the waterbox and an outlet influid communication with the second chamber of the waterbox; a secondbypass conduit having an outlet in fluid communication with the circuitfluid outlet of the evaporator assembly and an inlet in fluidcommunication with the third chamber of the waterbox; and a secondmultiple pass circuit fluid-to-refrigerant heat exchanger of the secondevaporator having an inlet in fluid communication with the secondchamber of the waterbox and an outlet in fluid communication with thethird chamber of the waterbox.

In any embodiment, the cooling fluid may be cooling water and thecircuit fluid may be chiller water. In any embodiment, the cooling fluidmay be cooling water and the circuit fluid may be chiller brine.Additionally, in any embodiment, the condenser assembly may also be ainclude a waterbox disposed intermediate the first condenser and thesecond condenser, a multiple pass cooling fluid-to-refrigerant heatexchanger in the second condenser having an outlet in fluidcommunication with the waterbox and an inlet in fluid communication withthe cooling fluid inlet of the condenser assembly, and a multiple passcooling fluid-to-refrigerant heat exchanger in the first condenserhaving an inlet in fluid communication with the waterbox and an outletin fluid communication with the cooling fluid outlet of the condenserassembly, with the cooling fluid inlet and the cooling fluid outletdisposed at opposite longitudinal ends of the condenser assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the disclosure, reference will be made tothe following detailed description which is to be read in connectionwith the accompanying drawing, where:

FIG. 1 is a plan view, in perspective, of an exemplary embodiment of adual circuit chiller in accordance with one aspect of the presentinvention applied to the evaporator water circuit;

FIG. 2 is an elevation view, in perspective, of the dual circuit chillerof FIG. 1;

FIG. 3 is a schematic illustration of the refrigerant circuits of theembodiment of the dual circuit chiller shown in FIG. 1;

FIG. 4 is a schematic illustration of the condenser waterside andevaporator waterside circuits of the embodiment of the dual circuitchiller shown in FIG. 1;

FIG. 5 is a elevation view, in cross-section, taken along line 5-5 ofFIG. 4;

FIG. 6 is a elevation view, in cross-section, taken along line 6-6 ofFIG. 4;

FIG. 7 is a schematic illustration of the condenser waterside and theevaporator waterside circuits in another exemplary embodiment of a dualcircuit chiller in accordance with an aspect of the invention;

FIG. 8 is a elevation view, in cross-section, taken along line 8-8 ofFIG. 7;

FIGS. 9A and 9B are elevation views, in cross-section, taken along line9A-9A and 9B-9B, respectively, of FIG. 7;

FIG. 10 is a schematic illustration of the condenser waterside and theevaporator waterside circuits in another exemplary embodiment of a dualcircuit chiller in accordance with an aspect of the invention;

FIG. 11 is a elevation view, in cross-section, taken along line 11-11 ofFIG. 7;

FIG. 12 is a schematic illustration of the evaporator waterside circuitin another exemplary embodiment of a dual circuit chiller in accordancewith an aspect of the invention;

FIG. 13 is a elevation view, in cross-section, taken along line 13-13 ofFIG. 12;

FIG. 14 is a elevation view, in cross-section, taken along line 14-14 ofFIG. 12;

FIG. 15 is a elevation view, in cross-section, taken along line 15-15 ofFIG. 12;

FIG. 16 is a elevation view, in cross-section, taken along line 16-16 ofFIG. 12;

FIG. 17 is a plan view of the embodiment of the intermediate waterboxdepicted in FIG. 12;

FIG. 18 is a perspective illustrating an alternate embodiment of theintermediate waterbox of the embodiment of the dual refrigerant circuitchiller depicted in FIG. 12;

FIG. 19 is a schematic illustration of the evaporator waterside circuitin another exemplary embodiment of a dual circuit chiller in accordancewith an aspect of the invention;

FIG. 20 is a plan view of the embodiment of the intermediate waterboxdepicted in FIG. 19;

FIG. 21 is a elevation view, in cross-section, taken along line 21-21 ofFIG. 19;

FIG. 22 is a elevation view, in cross-section, taken along line 21-21 ofFIG. 19;

FIG. 23 is a elevation view, in cross-section, taken along line 21-21 ofFIG. 19;

FIG. 24 is a elevation view, in cross-section, taken along line 24-24 ofFIG. 19;

FIG. 25 is a perspective illustrating the intermediate waterbox of theembodiment of the dual refrigerant circuit chiller depicted in FIG. 19;

DETAILED DESCRIPTION

Referring initially to FIGS. 1-4, 7 and 10 of the drawing, inparticular, there is depicted an exemplary embodiment of a compressionmachine 10 having two independent refrigerant circuits 100, 200 disposedin parallel refrigerant flow relationship, commonly referred to andreferred to herein as a dual circuit chiller. The chiller 10 includes awater-cooled condenser 30, a water-chilling evaporator 40, and a pair ofrefrigerant vapor compressors 120, 220. The refrigerant vaporcompressors 120, 220 may be centrifugal compressors. Separate drivemotors 122, 222 may be provided in operative association with the firstcompressor 120 and the second compressor 220, respectively. The firstdrive motor 122 drives only the first compressor 120. The second drivemotor 222 drives only the second compressor 220.

The condenser 30 comprises a first condenser 130 and a second condenser230 disposed in serial water flow relationship. Each of the firstcondenser 130 and the second condenser 230 comprises a coolingfluid-to-refrigerant, tube-in-shell heat exchanger having a plurality ofheat exchange tubes disposed within a longitudinally extending, closedcylindrical shell. The distal ends of the first and second condensers130, 230 are closed by end caps 134, 234, respectively, which aremounted to the tube sheets 136, 236, respectively. In the embodiment ofthe chiller 10 depicted in FIGS. 1-4, the respective proximal ends ofthe first condenser 130 and the second condenser 230 are interconnectedat respective tube sheets 32. However, in the embodiment of the chiller10 depicted in FIGS. 7 and 10, the respective proximal ends of the firstcondenser 130 and the second condenser 230 are interconnected to a waterbox 60 disposed between the respective tube sheets 32 of the first andsecond condensers 130, 230.

The evaporator 40 comprises a first evaporator 140 and a secondevaporator 240 disposed in serial water flow relationship. Each of thefirst evaporator 140 and the second evaporator 240 comprises a circuitfluid-to-refrigerant, tube-in-shell heat exchanger having a plurality ofheat exchange tubes disposed within a longitudinally extending, closedcylindrical shell. The distal ends of the first and second evaporators140, 240 are closed by end caps 144, 244, respectively, which aremounted to the tube sheets 146, 246, respectively. The respectiveproximal ends of the first evaporator 140 and the second evaporator 240are interconnected to a water box 50 disposed between the respectivetube sheets 42 of the first and second evaporators 140, 240.

As noted previously, the dual circuit chiller 10 has two independentrefrigerant circuits 100, 200 disposed in parallel relationship. Thefirst refrigerant circuit 100 includes the first compressor 120, thefirst condenser 130 and the first evaporator 140. In operation, highpressure, high temperature refrigerant vapor discharges from the firstcompressor 120 through discharge line 124 into the shell of the firstcondenser 130. The high pressure, high temperature refrigerant vaporintroduced into the shell of the first condenser 130 passes over theexterior of the heat exchange tubes therein in heat exchangerelationship with the cooling water passing through the heat exchangetubes, whereby the refrigerant vapor is cooled and condensed to a highpressure refrigerant liquid and the cooling water is heated. The highpressure, condensed refrigerant liquid passes from the first condenser130 to the first evaporator 140 through a refrigerant passage 111 inwhich is disposed an expansion device 125.

As the high pressure refrigerant liquid traverses the expansion device125, the refrigerant liquid expands to a lower pressure and a lowertemperature to form, most typically, a saturated mixture of refrigerantliquid and refrigerant vapor at the lower pressure and the lowertemperature. The lower pressure, lower temperature liquid/vapor mixtureis delivered via the passage 111 to and introduced into the shell of thefirst evaporator 140. The lower temperature refrigerant liquid collectsin the shell at least partially immersing the heat exchange tubes of thefirst evaporator 140. Thus, the chiller water passing through the tubesof the first evaporator 140 passes in heat exchange relationship withthe refrigerant introduced into the shell of the first evaporator 140,whereby the refrigerant liquid is heated and evaporated to a refrigerantvapor and the chilled water is cooled. The low pressure, low temperaturerefrigerant vapor passes from the first evaporator through suction line126 to return to the suction inlet of the first compressor 120.

The second refrigerant circuit 200 includes the second compressor 220,the second condenser 230 and the second evaporator 240. In operation,high pressure, high temperature refrigerant vapor discharges from thesecond compressor 220 through discharge line 224 into the shell of thesecond condenser 230. The high pressure, high temperature refrigerantvapor introduced into the shell of the second condenser 230 passes overthe exterior of the heat exchange tubes therein in heat exchangerelationship with the cooling water passing through the heat exchangetubes, whereby the refrigerant vapor is cooled and condensed to a highpressure refrigerant liquid and the cooling water is heated. The highpressure, condensed refrigerant liquid passes from the second condenser230 to the second evaporator 240 through a refrigerant passage 211 inwhich is disposed an expansion device 225.

As the high pressure refrigerant liquid traverses the expansion device225, the refrigerant liquid expands to a lower pressure and a lowertemperature to form, most typically, a saturated mixture of refrigerantliquid and refrigerant vapor at the lower pressure and the lowertemperature. The lower pressure, lower temperature liquid/vapor mixtureis delivered via the refrigerant passage 211 to and introduced into theshell of the second evaporator 240. The lower temperature refrigerantliquid collects in the shell at least partially immersing the heatexchange tubes of the second evaporator 240. Thus, the chiller waterpassing through the tubes of the second evaporator 240 passes in heatexchange relationship with the refrigerant introduced into the shell ofthe second evaporator 240, whereby the refrigerant liquid is heated andevaporated to a refrigerant vapor and the chilled water is cooled. Thelow pressure, low temperature refrigerant vapor passes from the secondevaporator 240 through suction line 226 to return to the suction inletof the second compressor 220.

In the embodiment depicted in FIG. 4, the heat exchange tubes of thefirst condenser 130 and of the second condenser 230 are arrayed in asingle pass arrangement. Condenser cooling water enters the condenser230 through the cooling water inlet 33 into an inlet chamber 31 definedwithin the end cap 234, thence passes serially first through the tubesof the second condenser 230 and thence through the tubes of the firstcondenser 130 into an outlet chamber 37 defined within the end cap 134of the first condenser 130. The cooling water passes out of the outletchamber 37 through the cooling water outlet 35. Thus, with respect tocooling water flow, the second condenser 230, which is part of thesecond refrigerant circuit 200, constitutes the upstream condenser, andthe first condenser 130, which is part of the first refrigerant circuit100, constitutes the downstream condenser.

The chiller water, that is the water to be chilled, enters theevaporator 40 through the chiller water inlet 45 of the first evaporator140 and exits the evaporator 40 through the chiller water outlet 43 ofthe second evaporator 240. Thus with respect to chiller water flow, thefirst evaporator 140, which is part of the first refrigerant circuit100, constitutes the upstream evaporator, and the second evaporator 240,which is part of the second refrigerant circuit 200, constitutes thedownstream evaporator. Therefore, the chiller water passes through theevaporator 40 in counter flow relationship to the condenser waterpassing through the condenser 30. In passing from the inlet chamber 41defined within the end cap 144 of the first evaporator 140 to the outletchamber 47 defined within the end cap 244 of the second evaporator 240,the chiller water does not traverse a single pass path as in a typicalconventional dual circuit chiller.

Rather in the chiller 10 of the invention, the chiller water flowingthrough the heat exchange tubes of the evaporator 40 traverses amultiple pass path in heat exchange relationship with the refrigerantwithin the evaporator 40. As depicted in FIGS. 4, 7 and 10, in thechiller 10, a waterbox 50 is provided between the respective tube sheets42 of the first and second evaporators 140, 240. The waterbox 50 ispartitioned by interior walls 52, 54 into three chambers, a firstchamber 51, a second chamber 53 and a third chamber 55.

In the embodiments depicted in FIGS. 4 and 10, the heat exchange tubesof the first pass tube bundle 171 of the first evaporator 140 connectthe inlet chamber 41 of the evaporator 40 in fluid flow communicationwith the first chamber 51 of the waterbox 50. The heat exchange tubes ofthe second pass tube bundle 172 of the first evaporator 140 connect thefirst chamber 51 of the waterbox 50 in fluid communication with theintermediate chamber 141 of the first evaporator 140. The heat exchangetubes of the third pass tube bundle 173 of the first evaporator 140connect the intermediate chamber 141 in fluid communication with thesecond chamber 53 of the waterbox 50. The heat exchange tubes of thefirst pass tube bundle 271 of the second evaporator 240 connect theintermediate chamber 53 of the waterbox 50 in fluid flow communicationwith the intermediate chamber 247 of the second evaporator 240. The heatexchange tubes of the second pass tube bundle 272 of the secondevaporator 240 connect the intermediate chamber 247 of the secondevaporator 140 in fluid communication with the third chamber 55 of thewaterbox 50. The heat exchange tubes of the third pass tube bundle 273of the second evaporator 240 connect the third chamber 55 of thewaterbox 50 in fluid communication with the outlet chamber 47 of thesecond evaporator 240. Thus, in the embodiment depicted in FIGS. 4 and10, the chiller water passing through the evaporator 40 traversesmultiple passes in each of the first and second evaporators 140, 240 inheat exchange relationship with the refrigerant therein.

In the embodiments of the chiller 10 as depicted in FIGS. 7 and 10, awaterbox 60 is also provided between the respective tube sheets 32 ofthe first and second condensers 130, 230. The waterbox 60 is partitionedby interior walls 62, 64 into three chambers, a first chamber 61, asecond chamber 63 and a third chamber 65. Condenser cooling water entersthe condenser 30 through the cooling water inlet 33 of the secondcondenser 230 and exits through the cooling water outlet 35 of the firstcondenser 130, and traverses a multiple pass path as the cooling waterflows through the condenser 30 in heat exchange relationship with therefrigerant.

In this multiple pass arrangement of the condenser 30, as depicted inFIGS. 7 and 10, the heat exchange tubes of the first pass tube bundle281 of the second condenser 230 connect the inlet chamber 31 of thecondenser 30 in fluid flow communication with the first chamber 61 ofthe waterbox 60. The heat exchange tubes of the second pass tube bundle282 of the second condenser 230 connect the first chamber 61 of thewaterbox 60 in fluid communication with the intermediate chamber 231 ofthe second condenser 230. The heat exchange tubes of the third pass tubebundle 283 of the second condenser 230 connect the intermediate chamber231 in fluid communication with the second chamber 63 of the waterbox60. The heat exchange tubes of the first pass tube bundle 181 of thefirst condenser 130 connect the intermediate chamber 63 of the waterbox60 in fluid flow communication with the intermediate chamber 137 of thefirst condenser 130. The heat exchange tubes of the second pass tubebundle 182 of the first condenser 130 connect the intermediate chamber137 of the first condenser 130 in fluid communication with the thirdchamber 65 of the waterbox 60. The heat exchange tubes of the third passtube bundle 183 of the first condenser 130 connect the third chamber 65of the waterbox 60 in fluid communication with the outlet chamber 37 ofthe first condenser 130. Thus, in the embodiment depicted in FIGS. 4 and8, the cooling water passing through the condenser 30 traverses multiplepasses in each of the first and second condensers 130, 230 in heatexchange relationship with the refrigerant therein.

Referring now to FIGS. 7, 9A and 9B, in particular, in the embodiment ofthe chiller 10 depicted therein, the chiller water enters the evaporator40 through a first bypass conduit 190 which extends longitudinally fromthe chiller water inlet through the first evaporator 140 to open influid communication with the first chamber 51 of the waterbox 50. Thechiller water exits the evaporator 40 through a second bypass conduit290 which extends longitudinally through the second evaporator 240 influid communication with the third chamber 55 of the waterbox 50 to thechiller water outlet. Between the first chamber 51 of the waterbox 50and the third chamber of the waterbox 50, the chiller water flowsthrough a two-pass heat exchanger in the first evaporator 140, throughthe second chamber 53 of the waterbox 50, and thence through a two-passheat exchanger in the second evaporator 240. The heat exchange tubes ofthe second pass tube bundle 172 of the first evaporator 140 connect thefirst chamber 51 of the waterbox 50 in fluid communication with theintermediate chamber 141 of the first evaporator 140. The heat exchangetubes of the third pass tube bundle 173 of the first evaporator 140connect the intermediate chamber 141 in fluid communication with thesecond chamber 53 of the waterbox 50. The heat exchange tubes of thefirst pass tube bundle 271 of the second evaporator 240 connect theintermediate chamber 53 of the waterbox 50 in fluid flow communicationwith the intermediate chamber 247 of the second evaporator 240. The heatexchange tubes of the second pass tube bundle 272 of the secondevaporator 240 connect the intermediate chamber 247 of the secondevaporator 240 in fluid communication with the third chamber 55 of thewaterbox 50.

Thus, in the embodiment depicted in FIG. 7, the chiller water passingthrough the evaporator 40 traverses two passes in each of the first andsecond evaporators 140, 240 in heat exchange relationship with therefrigerant therein, rather than three passes as in the embodimentsdepicted in FIGS. 4 and 10. Therefore, the chiller water in passingthrough the first evaporator 140 upon entering the evaporator 40 by wayof the bypass conduit 190 in effect bypasses a tube bundle prior toentering the first chamber 51 of the waterbox 50 and in passing throughthe second evaporator 240 by way of bypass conduit 290 in effectbypasses another tube bundle after leaving the third chamber 55 of thewaterbox 50 upon exiting the evaporator 40. Since the bypass conduits190, 290, provide a direct water flow path, respectively, between thechiller water inlet 45 and the first chamber 51 of the waterbox 50 andbetween the third chamber 55 of the waterbox 50 and the chiller wateroutlet 43, and since the bypass conduits 190, 290 have a very largeinside diameter as compared to the inside diameters of the individualheat exchange tubes of a tube bundle, the waterside pressure dropthrough the evaporator 40 of the FIG. 7 embodiment is significantlyreduced as compared to the waterside pressure drop associated withpassing through three tube bundle passes as in the evaporator 40 of theembodiments depicted in FIGS. 7 and 10. The use of bypass conduits 190,290 for receiving chiller water directly into the evaporator waterbox 50and for discharging chiller water directly from the evaporator water box50, respectively, enables the bypass conduit 190 to be connecteddirectly to a customer's chiller water retune pipe (not shown) and thebypass conduit 290 to be connected directly to a customer's chilledwater supply pipe (not shown). In this embodiment, because the bypassconduits 190 and 290 do not open into or pass through the respective endwaterboxes 48, the heat exchanger tubes of the tube bundles 172, 173,271, 272 may be accessed for servicing and removal, if necessary, simplyby removing the cover of the appropriate end waterbox, withoutdisconnecting the evaporator from the customer's chiller water system.

In the embodiment of the dual refrigerant circuit chiller 10 depicted inFIG. 4, each of the condensers 130, 140 has a single pass coolingwaterside circuit and each of the evaporators 140, 240 has a three passchiller waterside circuit. In the embodiment of the dual refrigerantcircuit chiller 10 depicted in FIG. 7, each of the condensers 130, 230has a three pass cooling waterside circuit and each of the evaporators140, 240 has a two pass chiller waterside circuit. In the embodiment ofthe dual refrigerant circuit chiller 10 depicted in FIG. 10, each of thecondensers 130, 230 has a three pass cooling waterside circuit and eachof the evaporators 140, 240 has a three pass chiller waterside circuit.In each of these configurations, the cooling water enters the condenser30 through one end cap and leaves the condenser 30 through its other endcap. Similarly, the chiller water enters the evaporator 40 through oneend cap and leaves the evaporator 40 through its other end cap. In thismanner, the series counterflow relationship between the condensing waterflow and the chiller water flow is maintained, even though the chillerwater circuit arrangement in the evaporator is multiple pass.Additionally, on the condenser side, the cooling waterside circuit maybe single pass or multiple pass while still maintaining a series flowarrangement through the condenser.

Referring now to FIGS. 12-18, in particular, in the embodiment of theevaporator 40 of chiller 10 depicted therein, the heat exchange tubes ofthe first pass tube bundle 371 of the first evaporator 140 connect theinlet chamber 341 of the first evaporator 140 in fluid flowcommunication with the first chamber 151 of the waterbox 150. The heatexchange tubes of the second pass tube bundle 372 of the firstevaporator 140 connect the first chamber 151 of the waterbox 150 influid communication with the intermediate chamber 343 of the end cap offirst evaporator 140. The heat exchange tubes of the bypass tube 390 ofthe first evaporator 140 connects the intermediate chamber 343 in fluidcommunication with the second chamber 153 of the waterbox 150. The heatexchange tubes of the first pass tube bundle 274 of the secondevaporator 240 connect the second chamber 153 of the waterbox 150 influid flow communication with the intermediate chamber 345 of the endcap of the second evaporator 240. The heat exchange tubes of the secondpass tube bundle 375 of the second evaporator 240 connect theintermediate chamber 345 of the second evaporator 240 in fluidcommunication with the third chamber 155 of the waterbox 150. The heatexchange tubes of the bypass conduit 690 of the second evaporator 240connect the third chamber 155 of the waterbox 150 in fluid communicationwith the outlet chamber 347 of the second evaporator 240.

In this embodiment, the waterbox 150, as illustrated in FIGS. 12 and 17,provides for passage of the chiller water through the second chamber 153in a generally vertical flow. Thus, the chiller water enters an upperregion of the second chamber 153 from the bypass conduit 390 of thefirst evaporator 140 and leaves the waterbox 150 at a lower region ofthe second chamber 153 to enter the first pass tube bundle 374 of thesecond evaporator 240. Therefore, in transitioning through the waterbox150 from the first evaporator 140 to the second evaporator 240, thechiller water is delivered to the lower pass tube bundle 374 of thesecond evaporator 240. An alternate embodiment of the waterbox 150providing for vertical passage of the chiller water in transitioningfrom the first evaporator 140 to the second evaporator 240 is depictedin FIG. 18. As depicted, a pair of internal walls 152 sections theinterior of the water box 150 into a first chamber 151, a second chamber153 and a third chamber 155. The respective tube bundle passes 371, 372,374, 375 and bypass conduits 390, 690 open into the waterbox 150 asdescribed above with respect to FIG. 12, with the second chamber 153providing the for the vertical transition.

Referring now to FIGS. 19-25, in particular, in the embodiment of theevaporator of chiller 10 depicted therein, the chiller water enters theevaporator 40 through a first bypass conduit 490 which extendslongitudinally from the chiller water inlet through the first evaporator140 to open in fluid communication with the first chamber 251 of thewaterbox 250. The chiller water exits the evaporator 40 through a secondbypass conduit 590 which extends longitudinally through the secondevaporator 240 in fluid communication with the third chamber 255 of thewaterbox 250 to the chiller water outlet. Between the first chamber 251of the waterbox 250 and the third chamber 255 of the waterbox 250, thechiller water flows through a two-pass heat exchanger in the firstevaporator 140, through the second chamber 253 of the waterbox 250, andthence through a two-pass heat exchanger in the second evaporator 240.The heat exchange tubes of the second pass tube bundle 472 of the firstevaporator 140 connect the first chamber 251 of the waterbox 250 influid communication with the end waterbox 448 of the first evaporator140. The heat exchange tubes of the third pass tube bundle 473 of thefirst evaporator 140 connect the end waterbox 448 in fluid communicationwith the second chamber 253 of the waterbox 250. The heat exchange tubesof the first pass tube bundle 474 of the second evaporator 240 connectthe intermediate chamber 253 of the waterbox 250 in fluid flowcommunication with the end waterbox 448 of the second evaporator 240.The heat exchange tubes of the second pass tube bundle 475 of the secondevaporator 240 connect the end waterbox 448 of the second evaporator 240in fluid communication with the third chamber 255 of the waterbox 250.

In the embodiment of the evaporator of chiller 10 depicted in FIG. 19,the bypass conduits 490, 590 do not open into or pass through therespective end waterboxes 448, but rather pass from the evaporator 40externally of the end waterboxes 448 in like manner to the bypassconduits 190, 290 shown in the FIG. 7 embodiment of the chiller 10.Thus, as discussed hereinbefore with respect to the FIG. 7 embodiment,the heat exchange tubes of the various tube bundles within theevaporator 40 may be serviced and removed, if necessary, simply byremoving the cover to the appropriate end waterbox 448, withoutdisconnecting the evaporator 40 from the customer's chiller watersystem. It is to be understood that the condenser 30 may also beconstructed in similar manner as discussed with reference to theevaporators 40 as depicted in FIG. 12 and FIG. 19.

It is to be understood that for purposes of simplifying the drawings,each of the tube bundles of the tube-in-shell heat exchangers in thecondensers and evaporator are represented in FIGS. 4, 7, 10, 12 and 19as a single tube to illustrate the flow path of the water and areillustrated in outline in the cross-sections shown in FIGS. 5, 6, 8, 13,14, 15, 16, 21, 22, 23 and 24. In reality, each tube bundle 171, 172,173, 271, 272, 273, 281, 282, 283, 371, 372, 374, 375, 472, 473, 474,475, comprises a large number of individual heat exchange tubes,typically numbering in the hundreds, extending in parallel relationshipbetween the tube sheets of each condenser and each evaporator, forexample as depicted with respect to tube bundles 172, 173, 271, 272 inFIGS. 9A and 9B. Each bypass conduit 190, 290, 390, 490, 590, 690defines a large flow area fluid passages relative to the flow areadefined by an individual tube of the tube bundles.

Although the chiller 10 has been described herein with reference towater as the condenser cooling fluid and water as the circuit fluid tobe chilled, it is to be recognized by those skilled in the art thatfluids other than water may be used as the circuit fluid and/or thecooling fluid in the dual refrigerant circuit chiller describedhereinabove and in the appended claims. As an example, in an embodiment,the circuit fluid may be chiller brine.

The terminology used herein is for the purpose of description, notlimitation. Specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as basis for teachingone skilled in the art to employ the present invention. While thepresent invention has been particularly shown and described withreference to the exemplary embodiments as illustrated in the drawing, itwill be recognized by those skilled in the art that variousmodifications may be made without departing from the spirit and scope ofthe invention. Those skilled in the art will also recognize theequivalents that may be substituted for elements described withreference to the exemplary embodiments disclosed herein withoutdeparting from the scope of the present invention.

Therefore, it is intended that the present disclosure not be limited tothe particular embodiment(s) disclosed as, but that the disclosure willinclude all embodiments falling within the scope of the appended claims.

1. A dual refrigerant circuit chiller comprising: a first refrigerantcircuit including a first condenser and a first evaporator; a secondrefrigerant circuit including a second condenser and a secondevaporator, a condenser assembly including the first condenser and thesecond condenser interconnected in a series cooling fluid circuit, thecondenser assembly having a cooling fluid inlet in fluid communicationwith the second condenser and a cooling fluid outlet in fluidcommunication with the first condenser; and an evaporator assemblyincluding the first evaporator and the second evaporator interconnectedin a series fluid circuit and a waterbox disposed intermediate the firstevaporator and the second evaporator, the evaporator assembly having acircuit fluid inlet in fluid communication with the first evaporator anda circuit fluid outlet in fluid communication with the secondevaporator, the first evaporator having a multiple pass circuitfluid-to-refrigerant heat exchanger having an outlet in fluidcommunication with the waterbox and an inlet in fluid communication withthe circuit fluid inlet of the evaporator assembly, the secondevaporator having a multiple pass circuit fluid-to-refrigerant heatexchanger having an inlet in fluid communication with the waterbox andan outlet in fluid communication with the circuit fluid outlet of theevaporator assembly, the circuit fluid inlet and the circuit fluidoutlet disposed at opposite longitudinal ends of the evaporatorassembly.
 2. The dual refrigerant circuit chiller as recited in claim 1wherein the circuit fluid-to-refrigerant heat exchanger of the firstevaporator and the circuit fluid-to-refrigerant heat exchanger of thesecond evaporator each comprise a three pass tube bundle heat exchanger.3. The dual refrigerant circuit chiller as recited in claim 1 whereinthe cooling fluid is cooling water and the circuit fluid is chillerwater.
 4. The dual refrigerant circuit chiller as recited in claim 1wherein the condenser assembly includes a waterbox disposed intermediatethe first condenser and the second condenser, a multiple pass coolingfluid-to-refrigerant heat exchanger in the second condenser having anoutlet in fluid communication with the waterbox and an inlet in fluidcommunication with the cooling fluid inlet of the condenser assembly,and a multiple pass cooling fluid-to-refrigerant heat exchanger in thefirst condenser having an inlet in fluid communication with the waterboxand an outlet in fluid communication with the cooling fluid outlet ofthe condenser assembly, the cooling fluid inlet and the cooling fluidoutlet disposed at opposite longitudinal ends of the condenser assembly.5. The dual refrigerant circuit chiller as recited in claim 1 whereinthe evaporator assembly further includes a first bypass conduit havingan inlet in fluid communication with the circuit fluid inlet of theevaporator assembly and an outlet in fluid communication with a firstchamber of the waterbox, and wherein the multiple pass circuitfluid-to-refrigerant heat exchanger of the first evaporator has an inletin fluid communication with the first chamber of the waterbox and anoutlet in fluid communication with a second chamber of the waterbox. 6.The dual refrigerant circuit chiller as recited in claim 5 wherein theevaporator assembly further includes a second bypass conduit having anoutlet in fluid communication with the circuit fluid outlet of theevaporator assembly and an inlet in fluid communication with a thirdchamber of the waterbox, and wherein the multiple pass circuitfluid-to-refrigerant heat exchanger of the second evaporator has aninlet in fluid communication with the second chamber of the waterbox andan outlet in fluid communication with a third chamber of the waterbox.7. A dual refrigerant circuit chiller comprising: a first refrigerantcircuit including a first condenser and a first evaporator; a secondrefrigerant circuit including a second condenser and a secondevaporator, a condenser assembly including the first condenser and thesecond condenser interconnected in a series cooling fluid circuit, thecondenser assembly having a cooling fluid inlet in fluid communicationwith the second condenser and a cooling fluid outlet in fluidcommunication with the first condenser; and an evaporator assemblyincluding the first evaporator and the second evaporator interconnectedin a series fluid circuit and a waterbox disposed intermediate the firstevaporator and the second evaporator, the waterbox having a firstchamber, a second chamber and a third chamber, the evaporator assemblyhaving: a circuit fluid inlet and the circuit fluid outlet disposed atopposite longitudinal ends of the evaporator assembly; a first bypassconduit having an inlet in fluid communication with the circuit fluidinlet of the evaporator assembly and an outlet in fluid communicationwith the first chamber of the waterbox; a first multiple pass circuitfluid-to-refrigerant heat exchanger disposed in the first evaporatorhaving an inlet in fluid communication with the first chamber of thewaterbox and an outlet in fluid communication with the second chamber ofthe waterbox; a second bypass conduit having an outlet in fluidcommunication with the circuit fluid outlet of the evaporator assemblyand an inlet in fluid communication with the third chamber of thewaterbox; a second multiple pass circuit fluid-to-refrigerant heatexchanger of the second evaporator has an inlet in fluid communicationwith the second chamber of the waterbox and an outlet in fluidcommunication with the third chamber of the waterbox.
 8. The dualrefrigerant circuit chiller as recited in claim 7 wherein the circuitfluid-to-refrigerant heat exchanger of the first evaporator and thecircuit fluid-to-refrigerant heat exchanger of the second evaporatoreach comprise a two pass tube bundle heat exchanger.
 9. The dualrefrigerant circuit chiller as recited in claim 7 wherein the coolingfluid is cooling water and the circuit fluid is water.
 10. The dualrefrigerant circuit chiller as recited in claim 7 wherein the coolingfluid is cooling water and the circuit fluid is brine.
 11. The dualrefrigerant circuit chiller as recited in claim 7 wherein the condenserassembly includes a waterbox disposed intermediate the first condenserand the second condenser, a multiple pass cooling fluid-to-refrigerantheat exchanger in the second condenser having an outlet in fluidcommunication with the waterbox and an inlet in fluid communication withthe cooling fluid inlet of the condenser assembly, and a multiple passcooling fluid-to-refrigerant heat exchanger in the first condenserhaving an inlet in fluid communication with the waterbox and an outletin fluid communication with the cooling fluid outlet of the condenserassembly, the cooling fluid inlet and the cooling fluid outlet disposedat opposite longitudinal ends of the condenser assembly.
 12. The dualrefrigerant circuit chiller as recited in claim 7 wherein the coolingfluid is cooling water and the circuit fluid is brine.
 13. The dualrefrigerant circuit chiller as recited in claim 1 wherein theintermediate waterbox is sectioned into a first chamber, a secondchamber, and a third chamber.
 14. The dual refrigerant circuit chilleras recited in claim 1 wherein the second chamber of the intermediatewaterbox provides a generally vertical flow passage through thewaterbox.
 15. The dual refrigerant circuit chiller as recited in claim 7wherein the first bypass conduit extends externally of the evaporatorassembly at a first end of the evaporator assembly for connection to afluid line for receiving circuit fluid and the second bypass conduitextends externally of the evaporator assembly at a second end of theevaporator assembly for connection to a fluid line for dischargingcircuit fluid.
 16. The dual refrigerant circuit chiller as recited inclaim 7 wherein the condenser assembly includes: a waterbox disposedintermediate the first condenser and the second condenser, the waterboxhaving a first chamber, a second chamber, and a third chamber; a firstbypass conduit having an inlet in fluid communication with the coolingfluid inlet of the condenser assembly and an outlet in fluidcommunication with the first chamber of the waterbox; a first multiplepass cooling fluid-to-refrigerant heat exchanger disposed in the secondcondenser having an inlet in fluid communication with the first chamberof the waterbox and an outlet in fluid communication with the secondchamber of the waterbox; a second bypass conduit having an outlet influid communication with the cooling fluid outlet of the condenserassembly and an inlet in fluid communication with the third chamber ofthe waterbox; a second multiple pass cooling fluid-to-refrigerant heatexchanger disposed in the first condenser having an inlet in fluidcommunication with the second chamber of the waterbox and an outlet influid communication with the third chamber of the waterbox.
 17. The dualrefrigerant circuit chiller as recited in claim 16 wherein the firstbypass conduit extends externally of the condenser assembly at a firstend of the condenser assembly for receiving cooling fluid and the secondbypass conduit extends externally of the condenser assembly at a secondend of the condenser assembly for discharging cooling fluid.